The present invention relates generally to a magnetic disk device for writing and reading information on and from a plurality of disk-like magnetic recording media with a plurality of magnetic recording heads. More specifically, the invention is concerned with a dummy write technique for coping with such situation in which a reproduced signal derived from the output of a magnetic head suffers as problem such as deformation of signal waveform.
When a waveform deformation or the like abnormality makes appearance in a reproduced signal of a magnetic head of a magnetic disk device, such approach has heretofore been taken that a recording current for a magnetic head suffering abnormality is gradually decreased from a time point immediately after write operation to thereby regenerate the magnetic head in an effort to suppress the waveform deformation of the reproduced signal, as disclosed in JP-A-5-282607. As another approach for solving the problem mentioned above, there has been proposed such technique that dummy write operation is conducted at specific addresses by using the magnetic head suffering abnormality for thereby suppressing the waveform deformation by regenerating concerned the magnetic head, as disclosed in JP-A-6-111218.
With the method taught in JP-A-5-28267, there arises necessity for providing areas for effectuating suppression of the waveform deformation in all of sectors, respectively. As a result of this, however, effective storage capacity of the magnetic disk device as a whole decreases, which is of course undesirable.
On the other hand, according to the technique disclosed in JP-A-6-111218, it is sufficient to allocate a dummy write area of one sector to each of the magnetic head. Accordingly, the problem of the effective storage capacity of the magnetic disk device being decreased can essentially be avoided. However, when the magnetic disk device is of an embedded-servo type, problems mentioned below will be encountered.
The magnetic disk device of the embedded-servo type features that read/write operation is performed by a magnetic head selected currently and that seeking operation and following operation for a target track are conducted on the basis of servo information written or recorded on a disk of concern at a predetermined location.
Now, let's assume that some abnormality or irregularity occurs in a given magnetic head of the embedded-servo type magnetic disk device, as a result of which waveform of the reproduced signal outputted from that magnetic head varies or deforms to such extent that data recorded on the magnetic recording disk surface can not be read out correctly. In that case, the seeking operation and following operation are attempted in an effort to perform a dummy write operation at a specific address. In reality, however, the servo information recorded on the magnetic recording disk surface can not be read out because of abnormality of the magnetic head and hence deformation of the waveform of the reproduced signal involving seeking error or following operation error.